1. Field of the Invention
This invention relates to a fastener and resilient grommet assembly for joining apertured work pieces. More particularly this invention relates to a bolt and rubber grommet assembly which allows relative movement or axial play between the bolt and grommet while retaining the bolt in the grommet.
2. Description of the Prior Art
There are a wide variety of fastener assemblies which combine a threaded fastener with a grommet or washer or both. The grommet is normally used for vibration isolation and sometimes to perform a sealing function. The washer protects the surface of one of the parts being joined or protects against the grommet being destroyed when the fastener is driven into the work or parts being joined. Grommets are typically retained on the shank of the screw or bolt by an elastic stretching, and a washer may be captured between the fastener head and the grommet. Washers can be retained independently of a grommet by keys or snapping a projection over a bead, rim, flange or the like. Pressing a metal washer over the shank of a metal fastener requires considerable force and is usually done in a press. In some instances, a forging, crimping, flaring or similar production step is utilized in retaining the washer. These assembly and post-assembly operations can add considerable expense to the fastener assembly which must be balanced against the ease in which the assembly is used in its intended joining function.
With the above-mentioned fastener assemblies, there is normally no need to provide anything more than a degree of radial play between the fastener and washer or grommet to satisfy a typical end use joining of parts. Consideration of providing axial movement or play between the fastener assembly parts is normally not needed. Likewise, providing means for retaining the fastener assembly on one of the parts to be joined is not a factor. However, with the increasing prevalence in the industry for producing and shipping preassembled subassemblies, particularly in the automotive field, the need for such retention and axial play features is becoming more apparent.
In prior art attempts to provide a fastener assembly which can be secured to one of the parts to be joined and which allows axial play or retractable movement of the fastener, metal standoff bushings have been used. Rubber grommets are either squeezed into the interior of the bushing or stretched over the exterior of the bushing as shown in U.S. Pat. Nos. 3,126,935 and 4,732,519 respectively. Both of these structures require flaring of the bushing for retention to one of the parts being joined. See, for example, FIG. 4 of U.S. Pat. No. 3,126,935, where a flaring tool is used on one side of the part in conjunction with a backup tool on the other side of the part. Considerable force must also be used in the fastener assembly of U.S. Pat. No. 4,732,519 to force the projections or wings on the bolt shank past the annular bead on the stand off bushing. Neither of these structures provide sealing of the bolt shank to the part aperture.